Aww. Sells-woman is such a pretty lady.
Yepp, that rooting part is harsh. The King is right. Sending her into a political marriage, that would have held her life as hostage and with possibly no love involved, was a mistake to begin with. Now, I do feel a bit for the ex-dad. He married and wanted a child. They had "intercourse" (that might actually have not been very satisfying/fulfilling) and I guess nothing afterwards. I do believe Olivia was a very presentable wife and that she took her job seriously, but also a bad spouse. Of course he wouldn't be happy in that marriage. If it's an arranged marriage (always a bad idea) and nothing follows afterwards (and I bet he noticed she didn't trust him), and you are allowed to marry a second women and this way you do have a fulfilling married life, it's no wonder he preferred his real wife over his 1st one. Olivia married for political reasons and her political position she did get and could have kept. So far she has no right to complain about his behavior towards her. It's a different story about her son.
They had a deal. Ex-Dad's family would gain a rank they didn't deserve, as far as I know. Both nations would have been bound by MC, no matter who's son he is. That was the whole point of it. But maybe he somehow knew, that either something was fishy or even the whole truth. Maybe she couldn't hypnotize him or he remembered later. Or a parental trade should have been inherrited by MC and didn't show up. Or he knew about that rooting thing and that she didn't root and therefore couldn't have had sex with him in first place. If he does know, it all makes sense. Some bitch tried to fool him and steal his families fortune away. And his own kingdom was okay with it. If this was his way to stick the finger to them, it's okay. If not he is just an arsehole, that got lucky.
Handling his "son" this way though was bad. He wasn't overly cruel or violent, but didn't explane shit to him and didn't treated him at least kindly, if he had to lie to him, because he was too young. Shame on him.
As for Olivia: Being married off and being told to root is unreasonable. Her decision to not do so is sound except for one point. She didn't root, because an old fart died? Really? You simply don't root, if you are unsure about the commitment. Maybe she just told that her father as an excuse, though. I don't blame her for not doing so. Not. On. Bit. Though not telling her husband about it and backstabbing him was cruel. Just play fair with open cards. He knows the deal. Simply tell him, it's a job and that he should get a second wife and own children. Raise her son with him and let him be promoted, while his own kids would inherit his old title and all the lands. Nothing lost, just favors gained. Simple.